PROJECT SUMMARY. Oxygen homeostasis is critical for cell survival, normal development, and tissue function. Low levels of oxygen (hypoxia) activate the transcription factors known as hypoxia-inducible factors (HIFs). HIFs are the key regulators of the adaptive response to hypoxia, regulating genes involved in metabolic reprograming, angiogenesis, pluripotency and differentiation, epithelial-to-mesenchymal transition (EMT), and apoptosis. Accordingly, HIF activity is critical during many pathological processes, including cancer progression, obesity, heart disease, and stroke. The work proposed here focuses on HIF1A with the immediate goal of significantly advancing our mechanistic knowledge of the cellular response to hypoxia, and the ultimate goal of illuminating novel therapeutic strategies for human pathologies driven by HIF1A. A detailed dissection of the molecular mechanisms by which HIF1A and its cofactors regulate gene expression, both directly and indirectly, as well as the identification of the key genes required for the cellular adaptation to hypoxia will be critical to fully understand how different cell types and tissues react to this stress, and to envision how these responses can be manipulated during the course of disease. Using a combination of genomic, molecular biology, and functional approaches, this research proposal aims to: Define mechanisms driving cell type-specific gene expression upon activation of HIF1A by hypoxia. Elucidate the mechanisms of action of HIF1A transcriptional coactivators. Identify and characterize genes required for cell survival in hypoxia.